@wootapa/object-evaluator-ol

Extension of @wootapa/object-evaluator with spatial operators for openlayers and ogc query output.

Usage no npm install needed!

<script type="module">
  import wootapaObjectEvaluatorOl from 'https://cdn.skypack.dev/@wootapa/object-evaluator-ol';
</script>

README

Object Evaluator - Openlayers

Building code for webgis applications that needs feature-filtering on both client and server can be a pain. Instead of ending up with scattered javascript mixed with fragile XML/CQL generators, this library attempts to alleviate this by providing a single interface where you define your rules. When done, simply evaluate the features or generate the equivalent CQL/XML for your OGC compliant server.

This library extends https://github.com/wootapa/wa-object-evaluator with spatial operators and is intended to be used with Openlayers 6+.

See Demo with WFS/WMS side by side.

Installation

New browsers and bundlers (es):

$ npm install --save @wootapa/object-evaluator-ol

Old browsers (umd):

<script src="https://unpkg.com/@wootapa/object-evaluator-ol"></script>
// waoe.ol.and() ...

Methods

Below is only the spatial methods. See base library for the standard operators available for comparing attributes.

Statics

  • defaultProjection(projection) - Sets default projection for all new builders. The projection is assumed to be known by OpenLayers and values are assumed to be transformed. Defaults to EPSG:3857.

Spatial operators

An operator value = valid geometry. See below for options.

  • intersects(value) - True when object intersects value.
  • disjoint(value) - True when object do not intersects value.
  • contains(value) - True when object completely contains value.
  • within(value) - True when object is completely within value.
  • distanceWithin(value, distance, greatCircle?) - True when object is no more than specified distance (in meters) from value. Requires a correct projection. Uses greatCircle by default.
  • distanceBeyond(value, distance, greatCircle?) - True when object is more than specified distance (in meters) from value. Requires a correct projection. Uses greatCircle by default.

Other

  • projection(projection) - Overrides the default projection for current builder.
  • asOgcCql(opts?) - Outputs as OGC CQL.
  • asOgcXML(opts?) - Outputs as OGC XML.

CQL/XML serializers take an optional object:

geometryName?, // Serializes operators with a different geometryName. Ex 'the_geom'.
projection?, // Serializes operators with a different projection. Ex 'EPSG:4326'.
decimals? // Rounds geometry decimal precision on serialized operators. Ex, 5.
useProjectionUnitForDistance? // Some backends ignores the unit part of dwithin/beyond filters. This converts meters to the unit of the projection.

What is a geometry?

  • ol/Feature (can carry attributes and respects geometryName)
  • ol/Geometry
  • An object with a valid ol/Geometry (ex feature.getProperties()) (can carry attributes)
  • WKT
  • GeoJSON (can carry attributes)
  • Array(2=point, 4=extent=polygon, 6=linestring, 8+=linestring/polygon)

Evaluating

When evaluating, make sure you pass a geometry that can carry attributes; or you will not be able to compare attributes using the standard operators. Got it? Great!

An example

So maybe you have a bunch of features and G√ľnter asked you for all wells.

const oe = and().eq('type', 'well').done();

You figure the depth must at least 32 meters

oe.gte('depth', 32).done()

Franz says it must be drilled before 1998

oe.lte('drilled', new Date(1998,0)).done()

Werner gives you the extent of the wells

oe.intersects([13.8517, 55.9646, 14.3049, 56.1017]).done() // <- You have options what you pass here.

In the end, this is the result.

const oe = and()
    .eq('type', 'well')
    .gte('depth', 32)
    .lte('drilled', new Date(1998,0))
    .intersects([13.8517, 55.9646, 14.3049, 56.1017])
    .done();

Apply on client features...

const features = [...];
const wells = features.filter(oe.evaluate);

...or output as CQL/XML and pass it to your OGC compliant server.

const opts = { geometryName: 'geom', projection: 'EPSG:3006', decimals: 0 }; // <- Optional
const cql = oe.asOgcCql(opts);
const xml = oe.asOgcXml(opts);

Pro ol-tip!

To hide/show features based on the result you can do:

const hiddenStyle = new Style();
source.forEachFeature(feature => {
    feature.setStyle(
        oe.evaluate(feature)
            ? null        // visible (use layer style)
            : hiddenStyle // hidden (overrides layer style)
        );
});